Pretoria, South Africa — The trial of Oscar Pistorius, the Olympian accused of murdering his girlfriend Reeva Steenkamp, got off to a dramatic start Monday with evidence that appeared to give prosecutors a strong start in a South African crime case being followed around the world.

Michelle Burger, a University of Pretoria lecturer, lives about 200 yards from Mr. Pistorius' residence, testified that she heard screaming and cries for help.

"I knew something terrible was happening in that house," she testified.

The prosecution asserts that Mr. Pistorius, a globally-renowned athlete who sprints on carbon-fiber blades, killed Ms. Steenkamp in a rage after the couple had a fight in the early morning hours on Valentine's Day a year ago.

Pistorius insists that he fired four shots through a locked toilet door in his Pretoria house because he thought an intruder was in the room. Instead, he hit Ms. Steenkamp, a law graduate and model, who died almost instantly.

Burger's account appears to run contrary to Pistorius's account. She said she was certain the woman's cries were followed by four shots, testimony implying that Pistorius knew who he was shooting at.

Burger is the first witness in what has been described as South Africa's OJ Simpson case, after the famous US football player who was sensationally acquitted in Los Angeles of murdering his ex-wife and her lover.

Last year, Pistorius appeared fragile and was frequently tearful in hearings. But today he strode into court dressed in a neatly-pressed black suit, white shirt, and black tie with a determined expression on his face, and spent the day scribbling notes furiously on a pad, often passing them to his legal team.

In a statement read to the court he attacked the prosecution's "untruthful" allegations and "unfair" methods, and insisted again that what happened was "a tragic accident."

"There was no argument," the statement read. "The allegation I wanted to shoot or kill Reeva could not be further from the truth."

Burger at times seemed tearful. She said she called to her husband to come back into the room to phone security. The couple then rang authorities to say there was "an attack in Silverwoods estate," where Pistorius lived.

"I heard screams again, it was worse, more intense," she said.

Asked to clarify the nature of the screams, Burger said the person screaming "was very scared. It was a scream that was a climax....It was very traumatic for me to hear those blood curdling screams. It leaves you cold to hear that angst, that fear."

Burger then stated she heard gun shots. There was a pause after the first shot, then three other shots. She said she thought the screaming continued as the firing went on.

"It was bang (pause), bang bang bang," Burger said. "Very shortly after the last shot was the last time I heard her voice."

He also pleaded not guilty to two previous charges of recklessly shooting a firearm in public, and of illegal possession of ammunition.

Seated behind the athlete in the public gallery were nine members of his family including his siblings Carl and Aimee Pistorius. Just yards away Steenkamp's mother, June, was seated.

As she walked into court this morning, June Steenkamp saw the man her daughter loved and was later killed by, for the first time. No words were exchanged between her and the Pistorius family, despite the close proximity. The defendant appeared never to look her way.

Ms. Steenkamp said in an interview over the weekend that she did not hate the athlete but would pray for him.

"I just want to look him in the eyes, and see for myself the truth about what he did to Reeva. And whatever the court decides at the end of his trial, I will be ready to forgive him," she told the London-based Daily Mail.